You can delete project files from your workspace without deleting the project from the depot. Files are removed but the project remains under Perforce control. Note that, to subsequently work on the project again, you must sync the files.
To delete files from your workspace, right-click the project and choose Team>Remove from Workspace. Note that you cannot edit the files after removing them from the workspace.
To restore the files, right-click the project and choose Team>Sync to Head.